Gas chromatography (GC) is a technique for separating molecules to allow for the detection and quantification of isolated species. The flame ionization detector (FID) is the most commonly used GC detector because of its ease of operation, robustness and high sensitivity to most carbon-containing molecules. The separation, detection and quantification of carbon-containing molecules, is efficiently and accurately done with gas chromatograph and flame ionization detection. However, current implementations of GC with FID (GC/FID) require the calibration of the response of the FID to particular molecules, which depends on the molecular structure, composition and concentration. Moreover, certain carbon-containing molecules have low or negligible response in the FID, including, for example, carbon monoxide (CO), carbon dioxide (CO2), carbon disulfide (CS2), carbonyl sulfide (COS), hydrogen cyanide (HCN), formamide (CH3NO), formaldehyde (CH2O) and formic acid (CH2O2).
The conversion of carbon-containing molecules at the exit of GC columns into methane (CH4) prior to their introduction into the FID increases the detection sensitivity to carbon-containing molecules and leads to similar per carbon responses of the FID regardless of the chemical origin of the methane. In one such embodiment, the GC column effluent is combusted in a palladium (Pd) containing reactor containing an oxygen or air co-feed, the resulting carbon monoxide (CO) and carbon dioxide (CO2) products are subsequently converted to methane in a reduction chamber containing nickel (Ni) and a hydrogen gas (H2) co-feed.
Prior art of interest includes a system used for testing GC machines by use of standards of known concentration and composition, involving two separate reaction vessels separated with a 4-port valve and tubing (T. Watanabe et al. “Development of a precise method for the quantitative analysis of hydrocarbons using post-column reaction capillary gas chromatography with flame ionization detection.” Chromatography, vol. 27 (Mar. 8, 2006), pp. 49-55.). This combustion reaction chamber utilized a commercially available palladium-asbestos catalyst packed into a stainless steel tube containing quartz wool. The reduction catalyst described by this system was a commercially available nickel catalyst for a methanizer packed into a stainless steel tube containing quartz wool. This system also included separate temperature controls and heating elements for the combustion and reduction chambers.
Other prior art of interest includes a system comprising multiple couplings, and H2 and air inlets outside of the heated block included in the system (S. Maduskar et al. “Quantitative carbon detector (QCD) for calibration-free, high resolution characterization of complex mixtures.” Royal Society of Chemistry, (November 2014) Lab on a Chip.). The system used a commercially available catalyst consisting of 10% Pd/alumina for the combustion chamber, and a commercially available nickel on diatomaceous earth catalyst for the reduction chamber.